The science potential of ALFA: Adaptive optics with natural and laser guide stars

¹ Max-Planck-Institut für extraterrestrische Physik, Postfach 1603, D-85740 Garching, Germany
² Max-Planck-Institut für Astronomie, Königstuhl 17, D-69117 Heidelberg, Germany
³ University of California, San Diego, Physics Dept., Center for Astrophysics & Space Sciences, Mail Code 0424, La Jolla, CA 92093-0424, U.S.A.
⁴ European Southern Observatory, Karl Schwarzschildstraße 2, D-85748, Garching, Germany

Send offprint request to: R. Davies: davies@mpe.mpg.de

Received: 12 February 1999
Accepted: 25 May 1999

Abstract

Adaptive optics with laser guide stars is mandatory in order to make use of the full capabilities of 8-m class telescopes. However, progress has been slow in two particular areas: techniques for spectroscopy at diffraction limited resolution and wavefront sensing on laser guide stars. ALFA – currently the only European laser guide star adaptive optics system, and the only one in the world open to guest observers – has made significant advances in both of these. In this paper we report on our first results from summer 1998, representing significant improvements over previous performance. We report on observations using natural guide stars which demonstrate that for bright stars () ALFA can now reach K-band Strehl ratios in excess of 60% and easily resolve binaries at the diffraction limit of the telescope. We then present some of the first integral field spectroscopy at diffraction limited scales, showing we are able to distinguish spectra of binary stars with a separation of only 0.26″. We also discuss results from a wide field image, which indicate that useful correction (allowing binary stars and circumstellar dust shells to be resolved) can be achieved from a relatively faint star to a radius of at least 1′. Our last set of results include a correction on a galaxy using the laser guide star as the reference. The best result to date is of the galaxy UGC 1347 in Abell 262. Correcting tip-tilt on a star 41″ away and higher orders on the laser, we achieved an increase in peak intensity of 2.5, and a reduction in FWHM from 1.07″ to 0.40″.